Jeremy, I've fetched v3-0-test branch from git and tried it.
To my surprise, the bug is still present there!
$ ./smbclient --version
Version 3.0.28a-GIT-086eaf2-test
Please let me know which kind of information I can provide to help you.

Jeremy,
I've found a problem and made a patch for it, please see the attachment.
On 'cd <relative_path>', CLI_DIRSEP_STR is appended to the directory's end.
But on 'cd <absolute_path>', CLI_DIRSEP_STR is not appended.
My patch changes it to always append CLI_DIRSEP_STR, whenever the path is relative or absolute.
Though it solves my problem, in no way this patch is final.
It is merely to point you at the problem.